“…This can be understood from the changes in components included in a with decreasing μ [19]. Figure 1Literature compilation of correlation between measured specific maintenance rates a and maximum relative growth rates μ max for various microbial species ( ж [1]; [10]; × [21];○ [22]; [23]; — [26]; [29]; [33]; [34]; [36]; [43]; [44]; [58]; [59]; + [60]).…”
Microbial maintenance is an important concept in microbiology. Its quantification, however, is a subject of continuous debate, which seems to be caused by (1) its definition, which includes nongrowth components other than maintenance; (2) the existence of partly overlapping concepts; (3) the evolution of variables as constants; and (4) the neglect of cell death in microbial dynamics. The two historically most important parameters describing maintenance, the specific maintenance rate and the maintenance coefficient, are based on partly different nongrowth components. There is thus no constant relation between these parameters and previous equations on this subject are wrong. In addition, the partial overlap between these parameters does not allow the use of a simple combination of these parameters. This also applies for combinations of a threshold concentration with one of the other estimates of maintenance. Maintenance estimates should ideally explicitly describe each nongrowth component. A conceptual model is introduced that describes their relative importance and reconciles the various concepts and definitions. The sensitivity of maintenance on underlying components was analyzed and indicated that overall maintenance depends nonlinearly on relative death rates, relative growth rates, growth yield, and endogenous metabolism. This quantitative sensitivity analysis explains the felt need to develop growth-dependent adaptations of existing maintenance parameters, and indicates the importance of distinguishing the various nongrowth components. Future experiments should verify the sensitivity of maintenance components under cellular and environmental conditions.
“…This can be understood from the changes in components included in a with decreasing μ [19]. Figure 1Literature compilation of correlation between measured specific maintenance rates a and maximum relative growth rates μ max for various microbial species ( ж [1]; [10]; × [21];○ [22]; [23]; — [26]; [29]; [33]; [34]; [36]; [43]; [44]; [58]; [59]; + [60]).…”
Microbial maintenance is an important concept in microbiology. Its quantification, however, is a subject of continuous debate, which seems to be caused by (1) its definition, which includes nongrowth components other than maintenance; (2) the existence of partly overlapping concepts; (3) the evolution of variables as constants; and (4) the neglect of cell death in microbial dynamics. The two historically most important parameters describing maintenance, the specific maintenance rate and the maintenance coefficient, are based on partly different nongrowth components. There is thus no constant relation between these parameters and previous equations on this subject are wrong. In addition, the partial overlap between these parameters does not allow the use of a simple combination of these parameters. This also applies for combinations of a threshold concentration with one of the other estimates of maintenance. Maintenance estimates should ideally explicitly describe each nongrowth component. A conceptual model is introduced that describes their relative importance and reconciles the various concepts and definitions. The sensitivity of maintenance on underlying components was analyzed and indicated that overall maintenance depends nonlinearly on relative death rates, relative growth rates, growth yield, and endogenous metabolism. This quantitative sensitivity analysis explains the felt need to develop growth-dependent adaptations of existing maintenance parameters, and indicates the importance of distinguishing the various nongrowth components. Future experiments should verify the sensitivity of maintenance components under cellular and environmental conditions.
“…According to Leenen et al (1997), suspended Nitrosomonas europaea cells have a decay rate of 0.09 and 0.43 day À1 in the absence of oxygen or ammonium, respectively. For instance, the decay rates presented by Leenen et al (1997) are very high and do not correspond to the finding that was discussed earlier, namely that AOB start very quickly after starvation to use fresh ammonia with similar rates to those before starvation. To remove these radicals, reducing equivalents are needed, which may increase the biomass decay rate.…”
Section: Autotrophic Decay and Maintenance Requirementsmentioning
In most natural environments as well as in engineered environments, such as wastewater treatment plants, ammonia-oxidizing bacteria (AOB) experience fluctuating substrate concentrations. Several physiological traits, such as low maintenance energy demand and decay rate, cell-to-cell communication, cell mobility, stable enzymes and RNAs, could allow AOB to maintain themselves under unfavourable circumstances. This review examines whether AOB possess such traits and how these traits might offer advantages over competing organisms such as heterotrophic bacteria during periods of starvation. In addition, within the AOB groups, differences exist in adaptation to and competitiveness under conditions of high or low ammonia or oxygen concentrations. Because these findings are of importance with regard to the ecology and activity of AOB in natural and engineered environments, concluding remarks are directed towards future research objectives that may clarify unanswered questions, thereby contributing to the general knowledge of the ecology and activity of ammonia oxidizers.
“…For example, bioreactors used for wastewater treatment include a biofilm containing bacterial cells fixed onto carriers (2,9,10,27,30) or gel beads (6,12,14,18,19). In such arrangements, only the surfaces of the carriers or beads have activity, because substrates and oxygen for the immobilized cells are supplied only from the surface (11,16,17,23,25,31). Recently, however, improved methods were described whereby the oxygen-rich surface of a gel was used to mediate aerobic reactions, while the oxygenpoor interior was used for anaerobic reactions (7,8,13,15,26).…”
To improve the cooperative removal of nitrogen by Nitrosomonas europaea and Paracoccus denitrificans, we controlled their distribution in a tubular gel. When ethanol was supplied inside the tubular gel as an electron donor, their distributions overlapped in the external region of the gel. By changing the electron donor from ethanol to gaseous hydrogen, the distribution of P. denitrificans shifted to the inside of the tube and was separated from that of N. europaea. The separation resulted in an increase of the oxidation rate of ammonia by 25%.
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